Asymmetric Encryption using Nodejs Crypto module

A library is not necessary. Enter crypto.

Here's little module you could use to encrypt/decrypt strings with RSA keys:

const crypto = require('crypto')
const path = require('path')
const fs = require('fs')

const encryptStringWithRsaPublicKey = function (toEncrypt, relativeOrAbsolutePathToPublicKey) {
  const absolutePath = path.resolve(relativeOrAbsolutePathToPublicKey)

  const publicKey = fs.readFileSync(absolutePath, 'utf8')
  const buffer = Buffer.from(toEncrypt)
  const encrypted = crypto.publicEncrypt(publicKey, buffer)

  return encrypted.toString('base64')
}

const decryptStringWithRsaPrivateKey = function (toDecrypt, relativeOrAbsolutePathtoPrivateKey) {
  const absolutePath = path.resolve(relativeOrAbsolutePathtoPrivateKey)

  const privateKey = fs.readFileSync(absolutePath, 'utf8')
  const buffer = Buffer.from(toDecrypt, 'base64')
  const decrypted = crypto.privateDecrypt(privateKey, buffer)

  return decrypted.toString('utf8')
}

module.exports = {
  encryptStringWithRsaPublicKey: encryptStringWithRsaPublicKey,
  decryptStringWithRsaPrivateKey: decryptStringWithRsaPrivateKey,
}

I would recommend not using synchronous fs methods where possible, and you could use promises to make this better, but for simple use cases this is the approach that I have seen work and would take.